Exemplary aspects of the present invention relate to a lighting device and a projector equipped with the same.
Related art projectors include a lighting device that emits illuminating light, an electro-optic modulating device that modulates illuminating light from the lighting device according to an image signal, and a projection lens used to project modulated light from the electro-optic modulating device for an image to be displayed.
A projector configured in this manner may have a projection image on display having almost homogeneous luminance distributions, a lighting device employing a so-called integrator optical system capable of irradiating an illuminated region where an image is to be formed with almost homogeneous light intensity distributions is used as the lighting device.
FIG. 7 is a schematic showing a related art lighting device when viewed from above. FIG. 8 is a schematic of a first lens array when viewed along a light-source optical axis. As is shown in FIG. 7, a related art lighting device 800 includes a light source device 810 having a light-emitting tube 820 and an ellipsoidal reflector 830, a collimator lens 840, a first lens array 850, a second lens array 860, and a superimposing lens 870. LA denotes an illuminated region in a liquid crystal device or the like.
Respective optical components are disposed in reference to a light-source optical axis 810ax (the central axis of a luminous flux emitted from the light source device 810). Specifically, the first lens array 850, the second lens array 860, and the superimposing lens 870 are disposed in such a manner that their centers almost agree with the light-source optical axis 810ax and become almost perpendicular to the light-source optical axis 810ax. 
In the related art lighting device 800 configured in this manner, the light-emitting tube 820 includes a light-emitting portion (arc) having a predetermined length in the direction of the light-source optical axis 810ax, and the center of the light-emitting portion is disposed in close proximity to the position of a focal point (first focal point) F1, which is one of two focal points of the ellipsoidal reflector 830 on the light-source optical axis 810ax closer to the ellipsoidal reflector 830. Light emitted from the light-emitting portion is reflected on a reflection surface 830R of the ellipsoidal reflector 830, and the reflection light goes incident on the first lens array 850 after it is changed to an illuminating luminous flux almost parallel to the light-source optical axis 810ax by the collimator lens 840 while traveling to the other focal point (second focal point) F2 farther from the ellipsoidal reflector 830.
As is shown in FIG. 8, the first lens array 850 includes a matrix (in this case, 10 rows×6 columns) of plural small lenses 852, each having a rectangular contour almost analogous to the shape of the illuminated region LA, and divides an almost parallel illuminating luminous flux from the light source device 810 into plural partial luminous fluxes by the plural small lenses 852. As with the first lens array 850, the second lens array 860 also includes a matrix of plural small lenses 862, each having a rectangular contour. The small lenses 862 in the second lens array 860 are aligned in correspondence with the small lenses 852 in the first lens array 850. Plural partial luminous fluxes emitted from the small lenses 852 in the first lens array 850 are thus condensed independently on the corresponding small lenses 862. Respective plural partial luminous fluxes emitted from the respective small lenses 862 in the second lens array 860 are then superimposed by the superimposing lens 870 to illuminate the illuminated region LA in the liquid crystal device or the like.
In the related art lighting device 800, when the parallelism of a luminous flux emitted from the light source device 810 is insufficient, the luminous flux is not able to pass through the small lenses 852 and 862 that correspond to each other in the first lens array 850 and the second lens array 860, respectively. Such being the case, the inventor has previously disclosed a technique to enhance the parallelism of a luminous flux emitted from the light source device 810 (for example, see JP-A-2000-347293).
A lighting device including the integrator optical system of this kind includes a type that uses a parabolic reflector capable of making light from the light-emitting tube parallel upon reflection, besides a type that makes light from the light-emitting tube parallel by combining the ellipsoidal reflector and the collimator lens as described above.
FIG. 9 is a schematic used to explain a problem with a lighting device using a parabolic reflector. For a lighting device using a parabolic reflector 880, as is shown in FIG. 9, in the case of a reflection surface 880R including a paraboloid of revolution of the parabolic reflector 880, an angle of incorporation (an angle about the light-source optical axis 810ax), θ, needed to guide radially emitted light from the light-emitting tube 820 to the collimator lens 840 becomes smaller than in the case of a reflection surface 830R including an ellipsoid of revolution of the ellipsoidal reflector 830. The lighting device using the parabolic reflector 880 therefore has a problem that efficiency of light utilization is lower than the lighting device using the ellipsoidal reflector 830. With this being the situation, a lighting device adopting an ellipsoidal reflector has been developed actively in recent years.
The lighting device using such an ellipsoidal reflector, however, has inhomogeneous light intensity distributions, and the distributions tend to be biased toward the light-source optical axis, which results in problems as follows.
FIG. 10 is a schematic showing loci of light in a lighting device in the related art using an ellipsoidal reflector. FIGS. 11(a) and 11(b) are schematics used to explain are images on the second lens array. FIG. 11(a) is a schematic showing are images when formed ideally on the second lens array, and FIG. 11(b) is a schematic showing arc images actually formed on the second lens array. As is shown in FIG. 11, the related art lighting device 800 using the ellipsoidal reflector 830 has illuminance distributions such that illuminance is high in the vicinity of the light-source optical axis 810ax and illuminance becomes lower with distances from the light-source optical axis 810ax. Hence, as is shown in FIGS. 11(a) and 11(b), the are images 864 formed on the second lens array 860, which are supposed to be fit within respective small lenses 862 as is shown in FIG. 11(a), are biased toward the proximity to the light-source optical axis 810ax as is shown in FIG. 11(b). This gives rise to a phenomenon that are images lie off the surrounding cells of the small lenses 862.
Lying-off parts of light that are not fit within the respective small lenses 862 in the second lens array 860 are not able to illuminate the illuminated region and are wasted, thereby causing loss in quantity of light. Lying-off parts of light referred to herein are equivalent to light that has failed to pass through the small lenses 852 and 862 corresponding to each other in the first lens array 850 and the second lens array 860, respectively.
In the related art lighting device 800, a luminous flux is thought to be able to pass through the small lenses 852 and 862 that correspond to each other in the first lens array 850 and the second lens array 860, respectively, by enhancing the parallelism of an illuminating luminous flux emitted from the collimator lens 840. In practice, however, for part of an illuminating luminous flux at the center in the vicinity of the light-source optical axis 810ax, it remains impossible to pass through the small lenses 852 and 862, and a need for enhancements has been arising.
To this end, the inventor has disclosed a lighting device 900 as another related art lighting device that is capable of separating respective are images, formed near the light-source optical axis by the small lenses in the first lens array, from each other (for example, see International Publication No. WO 02/088842). FIG. 12 is a schematic to describe another related art lighting device 900. As is shown in FIG. 12, another related art lighting device 900 is configured in such a manner that, of the entire reflection light reflected on a reflection surface 930R of an ellipsoidal reflector 930, at least optical paths L1 heading toward the center about a light-source optical axis 910ax are changed to optical paths L3 heading to a slightly outer side than optical paths L2 parallel to the light-source optical axis 910ax, by increasing a conical constant K of a hyperboloid of revolution 940A of a concave lens 940 used to make an illuminating luminous flux from the light source device 910 almost parallel.
According to another lighting device 900, are images in the vicinity of the light-source optical axis 910ax are separated more satisfactorily than in the related art lighting device 800. Hence, of the entire reflection light reflected on the reflection surface 930R of the ellipsoidal reflector 930, at least the light paths L1 heading-toward the center about the light-source optical axis 910ax are enabled to pass through small lenses that correspond to each other in the first lens array and the second lens array (neither is shown).